Condensed Consolidating Financial Information - Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Condensed consolidating statement of cash flows
Net cash provided by (used in) continuing operating activities	$ 174.8	$ 198.6
Investing activities:
Purchase of equipment and improvements	(64.7)	(36.9)
Proceeds from sale of dealerships	58.4	9.0
Acquisitions, net	(156.5)	(314.2)
Other	(6.3)
Net cash (used in) provided by continuing investing activities	(169.1)	(342.1)
Financing activities:
Net borrowings (repayments) of long-term debt	84.6	153.1
Net (repayments) borrowings of floor plan notes payable — non-trade	(4.8)	63.0
Repurchases of common stock	(50.0)	(2.7)
Dividends	(29.2)	(25.6)
Net cash provided by continuing financing activities	0.6	187.8
Net cash provided by discontinued operations	0.1	2.5
Effect of exchange rate changes on cash and cash equivalents	0.7	1.4
Net change in cash and cash equivalents	7.1	48.2
Cash and cash equivalents, beginning of period	45.7	24.0
Cash and cash equivalents, end of period	52.8	72.2
Penske Automotive Group | Reportable legal entities
Condensed consolidating statement of cash flows
Net cash provided by (used in) continuing operating activities	(23.0)	(17.1)
Investing activities:
Purchase of equipment and improvements	(1.1)	(0.4)
Other	(1.6)
Net cash (used in) provided by continuing investing activities	(2.7)	(0.4)
Financing activities:
Net borrowings (repayments) of long-term debt	(44.0)	47.0
Net (repayments) borrowings of floor plan notes payable — non-trade	1.0	(1.2)
Repurchases of common stock	(50.0)	(2.7)
Dividends	(29.2)	(25.6)
Distributions from (to) parent	147.9
Net cash provided by continuing financing activities	25.7	17.5
Guarantor Subsidiaries | Reportable legal entities
Condensed consolidating statement of cash flows
Net cash provided by (used in) continuing operating activities	137.0	127.1
Investing activities:
Purchase of equipment and improvements	(38.6)	(20.1)
Proceeds from sale of dealerships	55.9	9.0
Acquisitions, net		(199.2)
Net cash (used in) provided by continuing investing activities	17.3	(210.3)
Financing activities:
Net borrowings (repayments) of long-term debt	9.3	12.7
Net (repayments) borrowings of floor plan notes payable — non-trade	(43.2)	59.4
Distributions from (to) parent	(135.3)	0.7
Net cash provided by continuing financing activities	(169.2)	72.8
Net cash provided by discontinued operations	0.1	2.5
Net change in cash and cash equivalents	(14.8)	(7.9)
Cash and cash equivalents, beginning of period	14.8	9.4
Cash and cash equivalents, end of period		1.5
Non-Guarantor Subsidiaries | Reportable legal entities
Condensed consolidating statement of cash flows
Net cash provided by (used in) continuing operating activities	60.8	88.6
Investing activities:
Purchase of equipment and improvements	(25.0)	(16.4)
Proceeds from sale of dealerships	2.5
Acquisitions, net	(156.5)	(115.0)
Other	(4.7)
Net cash (used in) provided by continuing investing activities	(183.7)	(131.4)
Financing activities:
Net borrowings (repayments) of long-term debt	119.3	93.4
Net (repayments) borrowings of floor plan notes payable — non-trade	37.4	4.8
Distributions from (to) parent	(12.6)	(0.7)
Net cash provided by continuing financing activities	144.1	97.5
Effect of exchange rate changes on cash and cash equivalents	0.7	1.4
Net change in cash and cash equivalents	21.9	56.1
Cash and cash equivalents, beginning of period	30.9	14.6
Cash and cash equivalents, end of period	$ 52.8	$ 70.7